linux-kernel - RE: [PATCH v11 00/23] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC)

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Message-ID: <SJ1PR11MB6083DDA12763F210D4378CEBFCFA2@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Tue, 18 Feb 2025 19:08:23 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Chatre, Reinette" <reinette.chatre@...el.com>, "babu.moger@....com"
	<babu.moger@....com>, Peter Newman <peternewman@...gle.com>
CC: "Moger, Babu" <bmoger@....com>, Dave Martin <Dave.Martin@....com>,
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	<x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>, "paulmck@...nel.org"
	<paulmck@...nel.org>, "akpm@...ux-foundation.org"
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	"Wieczor-Retman, Maciej" <maciej.wieczor-retman@...el.com>, "Eranian,
 Stephane" <eranian@...gle.com>
Subject: RE: [PATCH v11 00/23] x86/resctrl : Support AMD Assignable Bandwidth
 Monitoring Counters (ABMC)

> >> Based on the discussion so far, it felt like it is not a group level
> >> breakdown. It is kind of global level breakdown. I could be wrong here.
> >>
> >> My understanding so far, MPAM has a number of global counters. It can be
> >> assigned to any domain in the system and monitor events.
> >>
> >> They also have a way to configure the events (read, write or both).
> >>
> >> Both these feature are inline with current resctrl implementation and can
> >> be easily adapted.
> >>
> >> One thing I am not clear why MPAM implementation plans to create separate
> >> files(dynamically) in /sys/fs/resctrl/info/L3_MON/ directory to read the
> >> events. We already have files in each group to read the events.
> >>
> >> # ls -l /sys/fs/resctrl/mon_data/mon_L3_00/
> >> total 0
> >> -r--r--r--. 1 root root 0 Feb 17 08:16 llc_occupancy
> >> -r--r--r--. 1 root root 0 Feb 17 08:16 mbm_local_bytes
> >> -r--r--r--. 1 root root 0 Feb 17 08:16 mbm_total_bytes
> >
> > It would be nice if the filenames here reflected the reconfigured
> > events. From what I can tell on AMD with BMEC it is possible to change the
> > underlying events so that local b/w is reported in the mbm_total_bytes
> > file, and vice versa. Or an event like:
> >
> >    6       Dirty Victims from the QOS domain to all types of memory
> >
> > is counted.
> >
> > Though maybe we'd need to create a lot of filenames for the 2**6
> > combinations of bits.
>
> Instead of accommodating all possible names resctrl could support
> "generic" names as hinted in Dave Martin's proposal.
>
> The complication with BMEC is that these are the underlying
> mbm_local_bytes and mbm_total_bytes events on which configuration
> was built. Specifically, by default and at hardware reset mbm_local_bytes
> counts exactly that. The event is fixed if BMEC is not supported and
> configurable if it is.

Would if be possible to rename the files if the config changed?

I.e. initially they are named mbm_local_bytes and mbm_total_bytes.

But when the user changes the config for mbm_total_bytes using the
BMEC config file, that file is renamed everywhere to "user_config1"

-Tony